It has been known for many years that cellulose can be synthesized by certain bacteria, particularly those of the genus Acetobacter. However, taxonomists have been unable to agree upon a consistent classification of the cellulose producing species of Acetobacter. For example, the cellulose producing microorganisms listed in the 15th Edition of the Catalog of the American Type Culture Collection under accession numbers 10245, 10821 and 23769 are classified both as Acetobacter aceti subsp. xylinum and as Acetobacter pasteurianus. For the purposes of the present invention any species or variety of bacterium within the genus Acetobacter that will produce cellulose under agitated conditions should be regarded as a suitable cellulose producer for the purposes of the present invention.
Acetobactor aceti subsp. xylinum is normally cultured under static conditions with the cellulose microfibrils being produced at the air medium interface. A normal cellulose pellicle produced in a static culture tends to have a lamellar structure with significantly less branching. Most bacteria of this species are very poor cellulose producers when grown in agitated culture. One reason proposed for such poor production is that an agitated culture induces a tendency to mutation to noncellulose producing strains. In contrast, the Acetobacter strains according to the present invention are characterized by an ability to produce large amounts of cellulose in agitated culture without manifesting instability leading to loss of cellulose production in culture.
The present invention involves the processing and use of bacterial cellulose produced by such microorganisms under agitated conditions. U.S. Pat. No. 4,863,565, granted Sep. 5, 1989 discloses Acetobacter varieties which are vigorous cellulose producers under agitated culture conditions. The cellulose produced by the microorganisms and culture conditions disclosed in this application appears to be a unique type, physically quite different from the bacterial cellulose produced in static cultures. It has a highly branched, three dimensional reticulated structure.
Bacterial cellulose fibers formed from an agitated mixture is in the form of pellets or pellet fragments. These pellets may be on the order of 1 mm. in size. The pellets or pellet fragments are then formed in a cake which is typically between 10 and 20% solids. Before use the reticulated bacterial cellulose is diluted to the desired solids content, and soluble or insoluble materials are added to preserve or enhance the properties of the final product.
U.S. Pat. No. 4,861,427 discloses the use of such a bacterial cellulose as a surface treatment for fibrous webs.
U.S. Pat. No. 4,374,702 discloses a process in which a Gaulin homogenizer is used to convert wood pulp fibers to microfibrillated cellulose.